System and method of electric vehicle wireless charger output protection using zero voltage switching

ABSTRACT

A wireless charger output protection system and method is provided for protecting a battery in an electric vehicle during wireless charging. A wireless power transfer system includes a wireless charger on the electric vehicle side that receives power wirelessly from a charging base. The wireless charger output protection system and method shuts down the wireless charger output and dumps energy in a receive antenna (e.g., a vehicle pad) when a charging error is detected before the charging base can be shut down. The system and method employs a zero-voltage switching (ZVS) scheme to shut down the wireless charger output, in response to the charging error, to protect the switching devices and enhance overall reliability.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No. 15/795,825, filed Oct. 27, 2017, the disclosure of which is hereby incorporated in its entirety by reference herein.

TECHNICAL FIELD

The present disclosure relates to a wireless charger output protection scheme for an electric vehicle battery using a zero voltage switching (ZVS) system and method.

BACKGROUND

Wireless power transfer systems enable power to be transferred wirelessly from a source to a load. Inductive power transfer is a non-radiative, or near-field, type of wireless power transfer. Inductive power transfer uses an oscillating current passing through a primary coil (i.e., a transmit antenna) of a source to generate an oscillating magnetic near-field that induces currents in a secondary coil (i.e., a receive antenna) of a load. The source includes a power converter having power transistor switches which switch at controllable times to convert power of the source into the oscillating current passing through the primary coil.

Inductive power transfer is performed to wirelessly charge a load, such a traction battery of an electric vehicle, using power from the source. In such wireless electric vehicle charging systems, the transmit antenna of the source is embedded in a “charging” mat and the receive antenna (and an associated rectifier) is embedded in a designated location of the vehicle. The inductive power transfer involves inductive coupling between the antennas. For inductive power transfer to be efficient, the spacing between the antennas must be relatively close within small offset tolerances.

An electric vehicle requires frequent charging of the traction battery. In wired charging connections, an electric vehicle's on-board charger is connected to electric vehicle supply equipment (EVSE), such as a charging station, using a cordset plugged into a vehicle's charging port. A wired control loop between the on-board charger and the EVSE is used to monitor the battery charger output while the cordset is plugged in to the charging port. Upon a detection of any unexpected problems, the control loop may immediately shut down the output from the charging station to protect the traction battery from damage. In wireless charging systems, the control loop is likewise wireless, relying on near-field communication protocols such as WiFi, Bluetooth, etc. to communicate with the power source. Due to its nature, wireless communication is generally slower than wired connections. In the event of a charging error, the source may be relatively slow to respond by shutting down. This delay may cause damage to expensive vehicle batteries and high-power electronics.

SUMMARY

One or more embodiments of the present disclosure is directed to a wireless charger output protection system, which may include a powerline, a rectifier, a powerline sensor, a switch, and a switch controller. The powerline may transmit AC current induced in a receive antenna. The rectifier may rectify the AC current from the powerline into a DC power for charging a vehicle battery. The powerline sensor may be configured to output a voltage signal indicative of a powerline voltage. The switch may be connected to the powerline and may control electrical connection between the receive antenna and the rectifier. The switch controller may be connected to the powerline sensor, the switch, and a monitoring circuit. Further, the switch controller may receive an error signal indicative of a charging error from the monitoring circuit and may output a switch control signal causing the switch to change state, in response to the error signal, when the voltage signal received from the powerline sensor indicates a zero-voltage crossing point.

One or more additional embodiments of the present disclosure is directed to a method for switching off a wireless charger output. The wireless charger may include a powerline for transmitting AC power, a rectifier for converting the AC power from the powerline into DC power, and a powerline sensor in sensing relation to the powerline for outputting a signal indicative of a powerline voltage. The method may comprise: receiving, at a switch controller, an error signal indicative of a charging error from a battery monitoring circuit; receiving, at the switch controller, a voltage signal indicative of the powerline voltage; and outputting, by the switch controller in response to the error signal, a switch control signal to a switch connected to the powerline causing the switch to change state and disconnect the powerline from a vehicle battery when the voltage signal indicates a zero-voltage crossing point.

One or more additional embodiments of the present disclosure is directed to an apparatus for shutting down wireless charging of a vehicle battery. The apparatus may include a switch controller, configured to: receive an error signal from a monitoring circuit, indicative of a charging error; receive a voltage signal, from a powerline sensor, indicative of a powerline voltage of a powerline; and output a switch control signal, in response to the error signal, to a switch causing the switch to change state and disconnect the powerline from a vehicle battery when the voltage signal indicates a zero-voltage crossing point.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic diagram of an inductive power transfer system for wirelessly charging an electric vehicle with power from a charging base;

FIG. 2 illustrates a block diagram of an inductive power transfer system;

FIG. 3 illustrates a block diagram of wireless charger at the vehicle side having a ZVS controller according to one embodiment of the present disclosure;

FIG. 4 illustrates plots of various voltage waveforms at the vehicle side of the charging system;

FIG. 5 illustrates a plot showing the voltage waveform having a grace period of ZVS control; and

FIG. 6 illustrates a flowchart describing the operation of the method of the vehicle charging controller.

DETAILED DESCRIPTION

Detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the present invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.

Referring now to FIG. 1, a schematic diagram of an inductive power transfer system 10 for wirelessly charging an electric vehicle 12 with power from a charging base 14 is shown. The charging base 14 includes a transmit antenna 16 positioned in the ground or on the floor of a structure. The transmit antenna is sometimes referred to a base pad or mat due to its physical configuration. The vehicle 12 includes a receive antenna 18, often referred to as a vehicle pad, mounted to the underside of the vehicle. The transmit antenna 16 and the receive antenna 18 are aligned in close arrangement when the vehicle 12 is properly parked. Power of the charging base 14 can thus be transferred from the transmit antenna 16 to the receive antenna 18 for charging the vehicle 12. The receive antenna 18 is connected to the traction battery or the like of the vehicle 12. The power wirelessly transferred from the charging base 14 to the vehicle 12 is used to charge the traction battery.

A coordinate system 20 is also shown in FIG. 1. In the coordinate system 20, the transmit antenna 16 and the receive antenna 18 are separated along the z-direction when the vehicle 12 is parked over the transmit antenna 16. The vehicle 12 (particularly the receive antenna 18) can be displaced relative to the transmit antenna 16 along either the x-direction and the y-direction (i.e., relative to the ground or floor in which the transmit antenna 16 is positioned). Displacement of the receive antenna 18 from a preset optimal aligned position relative to the transmit antenna 16 in any of the coordinate directions decreases the efficiency with which power can be wirelessly transferred from the transmit antenna to the receive antenna. In this regard, displacement of the receive antenna 18 relative to the transmit antenna 16 changes the impedance seen by the power generating component of the charging base 14 that feeds the transmit antenna 16 with power.

Referring now to FIG. 2, with continual reference to FIG. 1, a block diagram of the inductive power transfer system 10 is shown. As shown in FIG. 2, in addition to the transmit antenna 16, the charging base 14 of the inductive power transfer system 10 includes an AC (alternating current) power source 22, an AC/DC (alternating current/direct current) rectifier 24, a DC/AC power converter 26, and a resonant network 28. The power source 22 provides AC power to the rectifier 24. The rectifier 24 rectifies the AC power to DC power and provides the DC power to the power converter 26. The power converter 26 converts the DC power into AC power and provides the AC power to the resonant network 28.

The transmit antenna 16 includes one or more coils (i.e., primary coil 30). The receive antenna 18 of the vehicle 12 includes one or more coils (i.e., secondary coil 32). The primary coil 30 and the secondary coil 32 are physically arranged next to one another (i.e., “loosely coupled”) when the vehicle 12 is properly parked. That is, the secondary coil 32 wirelessly couples with the primary coil 30 when the secondary coil is in the coupling-mode region of the primary coil providing a mutual inductance M and resonating at substantially the same frequency as the primary coil. The AC power from power converter 26 passes through the resonant network 28 and through the primary coil 30 and causes the primary coil to generate an oscillating magnetic near-field. The oscillating magnetic near-field induces currents in the secondary coil 32. The currents in the secondary coil 32 generate AC power on the vehicle side. As such, an inductive coupling between the primary coil 30 and the secondary coil 32 occurs for inductive power transfer from the charging base 14 to the vehicle 12.

As further shown in FIG. 2, in addition to the receive antenna 18, the vehicle 12 may include a vehicle charging unit 34. Together, the receive antenna 18 and the vehicle charging unit 34 may be referred to as a wireless charger 36. The vehicle charging unit 34 delivers power to a load of the vehicle 12 such as a vehicle battery 38 (i.e., traction battery).

FIG. 3 is a block diagram of the vehicle side of the inductive power transfer system illustrated in FIG. 2 illustrating the vehicle charging unit 34 in greater detail. As shown, the vehicle charging unit 34 may be connected to the vehicle battery 38 at a wireless charger output 40. As previously described, the currents induced in the secondary coil 32 of the receive antenna 18 generate AC power on the vehicle side. The AC power is delivered to the vehicle charging unit 34 along a powerline 42. The vehicle charging unit 34 may include a rectifier 44 that rectifies the AC power into DC power. The DC power from the rectifier 44 may be supplied to the vehicle battery 38 through, for example, a filter 46. This DC power at the wireless charger output 40 charges the vehicle battery 38.

The powerline 42 may include a positive powerline conductor 42 a for receiving the positive output from the receive antenna 18 and a negative powerline conductor 42 b for receiving the negative output from the receive antenna. Together, positive powerline conductor 42 a and the negative powerline conductor 42 b deliver the AC power to the rectifier 44. Accordingly, during wireless charging, the positive powerline conductor 42 a may receive a positive powerline conductor voltage V_(p+) and the negative powerline conductor 42 a may receive a negative powerline conductor voltage V_(p−). The positive powerline conductor voltage V_(p+) and the negative powerline conductor voltage V_(p−) are half sine waves that are 180 degrees out of phase (FIG. 4).

The vehicle charging unit 34 may further include powerline sensors 48 in sensing relation (e.g., connected) to the powerline 42 for detecting a powerline voltage. For example, a positive powerline sensor 48 a may be in sensing relation to the positive powerline conductor 42 a and a negative powerline sensor 48 b may be in sensing relation to the negative powerline conductor 42 b. The positive powerline sensor 48 a may detect the positive powerline conductor voltage V_(p+) and the negative powerline sensor 48 b may detect the negative powerline conductor voltage V_(p−). The powerline sensors 48 may be further configured to output voltage signals indicative of the powerline voltage. For instance, the positive powerline sensor 48 a may output a positive voltage signal V_(zero+) indicative of the positive powerline conductor voltage V_(p+) and the negative powerline sensor 42 b may output a negative voltage signal V_(zero−) indicative of the negative powerline conductor voltage V_(p−).

The vehicle charging unit 34 may also include a switch 50 connected to the powerline 42 configured to control electrical connection between the receive antenna 18 and the rectifier 44. With continuing reference to FIG. 3, the switch 50 may include a pair of switches, such as a positive switch 50 a and a negative switch 50 b. As shown, the positive switch 50 a may provide an ON/OFF connection between the negative powerline conductor 42 b and ground 52. Similarly, the negative switch 50 b may provide an ON/OFF connection between the positive powerline conductor 42 a and ground 52. During normal charging operation, the switches 50 a and 50 b may be open and the positive powerline conductor 42 a and negative powerline conductor 42 b connect the receive antenna 18 to the rectifier 44. The wireless charger output 40 to the vehicle battery 38 can be shut down by closing switches 50 a and 50 b and providing a direct path to ground for the electrical energy in the powerline 42, effectively disconnecting the rectifier 44 from the receive antenna 18. According to an embodiment, each switch 50 may be an IGBT (insulated gate bipolar transistor), though other types of switches may be employed such as a MOSFET (metal oxide semiconductor field effect transistor). The positive switch 50 a and the negative switch 50 b may be controlled by a switch controller 54. The switch controller 54 may be part of main controller of the vehicle charging unit 34 or may be a dedicated controller/control circuitry for controlling the state (i.e., open/close) of the switches 50 in response to inputs received at the switch controller 54.

As previously described, the control loop used to monitor the battery charger output in wired charging connections is relatively fast. Thus, if any unexpected problems occur during wired charging, the control loop may immediately shut down the output from the charging station to protect the battery from damage. In wireless charging systems, the control loop is likewise wireless, relying on relatively slower near-field communication protocols such as WiFi, Bluetooth, etc. to communicate with the AC power source 22 (FIG. 2). In the event of a charging error, the charging base 14 may be relatively slow to respond by shutting down the power source 22. This delay may cause damage to expensive vehicle batteries and high-power electronics. The switch controller 54 may allow the wireless charger output 40 to be shut down relatively quickly, by closing switches 50, before the wireless charging control loop can communicate a shutdown message to the charging base 14.

The switch controller 54 may be in communication with a monitoring circuit 56, such as a battery monitoring circuit, for monitoring the wireless charger output 40, the vehicle battery 38 itself, or the like for unexpected problems during normal wireless charging. Accordingly, the monitoring circuit 56 may be connected between the filter 46 and the vehicle battery 38 to monitor the wireless charger output 40. Alternatively, the monitoring circuit 56 may be connected to other parts of the charging circuit, such as the powerline, to monitor the charging of the battery 38. Additionally, the monitoring circuit 56 may be in communication with the in-vehicle network (e.g., CAN) to receive messages indicative of a charging error or other problem warranting the shutdown of the wireless charger output 40. As shown, the monitoring circuit 56 may be embedded in the vehicle charging unit 34. However, the monitoring circuit 56 may be an external module in communication with the switch controller 54. If a charging error is detected by the monitoring circuit 56, the monitoring circuit 56 may send an error signal V_(e) indicative of the charging error to the switch controller 54. As examples, the charging error may indicate one or more of the following conditions: over voltage, over current, microprocessor watchdog error, over temperature, in-vehicle network communication error, base unit error, and wireless communication error.

Responsive to the error signal V_(e) from the monitoring circuit 56, the switch controller 54 may output a switch control signal causing the switches 50 to change state (e.g., from opened to closed). As previously described, this quickly and effectively shuts down the wireless charger output 40 to protect the vehicle battery 38 from damage due to the error conditions without having to wait for the wireless control loop to complete its path to the charging base 14. To this end, the switch controller 54 may output a positive switch control signal V_(g+) to the positive switch 50 a causing it to change state (i.e., close) in response to the error signal V_(e). Similarly, the switch controller 54 may output a negative switch control signal V_(g−) to the negative switch 50 b causing it to change state (i.e., close) in response to the error signal. In the case of IGBT switches, the respective switch control signals may be received at the gate, providing a path to ground between the collector and emitter.

Although the switches 50 may be controlled to turn on/off at any time, turning on (i.e., closing) the switches while the respective powerline conductors are still at high voltage may result in a high voltage (e.g., up to approximately 850 volts peak) between the collector and the emitter (for an IGBT switch). In turn, this may result in a very high dI/dt transient current, which can be damaging to the switches, greatly reducing their lifespan. To improve switch reliability, and hence reliability of the wireless charger output protection system, a zero-voltage switching (ZVS) control scheme may be employed to shut down the wireless charger output 40. Under the ZVS control scheme, the switches 50 may only be turned ON (i.e., closed) when the powerline conductor voltages reach zero voltage, referred to as a zero-voltage crossing point. ZVS may increase switch reliability while allowing energy from the receive antenna 18 to be dumped to protect the vehicle battery 38.

Accordingly, the switch controller 54 may be configured to control the zero-voltage switching on the powerline conductors 42. To implement ZVS control, the switch controller 54 may be connected to both positive powerline sensor 48 a and negative powerline sensor 48 b. According to an embodiment, in response to the error signal V_(e), the switch controller 54 may output the negative switch control signal V_(g−) to the negative switch 50 b causing it to change state (i.e., close) when the positive voltage signal V_(zero+) indicative of the positive powerline conductor voltage V_(p+) from positive powerline sensor 48 a indicates a zero-voltage crossing point. Likewise, in further response to the error signal V_(e), the switch controller 54 may output the positive switch control signal V_(g+) to the positive switch 50 a causing it to change state (i.e., close) when the negative voltage signal V_(zero−) indicative of the negative powerline conductor voltage V_(p−) from negative powerline sensor 48 b indicates a zero-voltage crossing point.

FIG. 4 illustrates a series of timing diagrams plotting various voltage waveforms at the vehicle side of the wireless charging system. Plots 400B and 400C illustrate the waveforms of the positive powerline voltage V_(p+) and the positive sensor voltage V_(zero+), respectively. The positive sensor voltage V_(zero+) may be substantially in phase with the positive powerline voltage V_(p+) because the positive powerline sensor 48 a has a mostly resistive component. Compared to the positive powerline voltage V_(p+), the positive sensor voltage V_(zero+) may have a much smaller amplitude (e.g. at around 3V peak), as it is used as a control input to the switch controller 54. Plots 400F and 400G illustrate the waveforms of the negative powerline voltage V_(p−) and the negative sensor voltage V_(zero−), respectively. The negative sensor voltage, V_(zero−) may be substantially in phase with the negative powerline voltage V_(p−) because the negative powerline sensor 48 b has a mostly resistive component. Compared to the negative powerline voltage V_(p−), the negative sensor voltage V_(zero−) may have a much smaller amplitude, as it too is used as a control input to the switch controller 54. As an example, the powerline voltages V_(p+) and V_(p−) may be both half sine waves that are out of phase by approximately 180 degrees. Since the sensor voltages V_(zero+) and V_(zero−) are in phase with the powerline voltages V_(p+) and V_(p−), respectively, they are likewise out of phase by approximately 180 degrees.

Plot 400A illustrates the waveform of a combined clock signal V_(clock) generated by the switch controller 54 using the powerline voltages. For instance, the switch control 54 may generate two individual clock signals 410 and 420 that together form the combined clock signal V_(clock). In particular, waveform 410 may represent a positive clock signal generated by the switch controller from the positive powerline voltage V_(p+) and waveform 412 may represent a negative clock signal generated by the switch controller from the negative powerline V_(p−). As illustrated in plot 400A, being a square wave, the clock signal V_(clock) loosely corresponds to the powerline voltages V_(p+) and V_(p−), except that the clock signal V_(clock) is slightly narrower than the corresponding powerline voltages. For instance, at time t_(a), the clock signal 412 a may have a rising edge triggered by the negative powerline voltage V_(p−) coming ON, as illustrated in plot 400F. The clock signal 412 a may have a falling edge at time t_(a)′, shortly before the negative powerline voltage V_(p−) crosses zero. At time t_(b), the next clock signal 410 b may be generated by the switch controller 54 and have a rising edge triggered by the positive powerline voltage V_(p+) coming ON, as illustrated in plot 400B. In addition, the negative switch control signal V_(g−) may be controlled by a rising edge of the positive clock signal 410, while the positive switch control signal V_(g+) may be controlled by a rising edge of negative clock signal 412.

Plot 400E illustrates the waveform of an error signal V_(e) received by the switch controller 54 from the monitoring circuit 56. As described in connection with FIG. 3, the error signal V_(e) may be indicative of a charging error. As an example, the error signal V_(e) may switch from low to high at time t₁, indicating a charging error is detected, and the wireless charger output should be shut down. In this example, t₁ may occur between t_(c), when a rising edge of positive clock signal 410 c is generated, and t₂. Responsive to the error signal V_(e), the vehicle charging unit 34 may wirelessly send a message using near-field communication protocols via a wireless module (not shown) to the charging base 14 to stop charging. However, as discussed above, due to the nature of the wireless communication, there may be a relatively lengthy delay between when the vehicle charging unit 34 sends the wireless message and when the charging base 14 actually shuts down. To protect the battery 38 from unwanted charging during this period of delay, the vehicle charging unit 34 may effectively disconnect the powerlines between the receive antenna 18 and the rectifier 44 on the vehicle side by using powerline switches 50 to dump the powerline energy to ground. This effectively shuts down the wireless charger output 40 with relatively little delay.

As shown in FIG. 4, the positive powerline conductor 42 a may be at a high voltage at t₁ when the error signal V_(e) goes high indicating a charging error. As discussed above, turning on the negative powerline switch 50 b at t₁ to redirect the power from the positive powerline conductor 42 a to ground may cause damages to the negative powerline switch 50 b. Therefore, as previously described, a ZVS protection scheme may be employed to activate the powerline switches 50. Accordingly, the switch controller 54 may wait until t₂, when the positive powerline voltage V_(p+) and the corresponding positive sensor voltage V_(zero+) reaches a zero-voltage crossing point, to close (turn on) the negative powerline switch 50 b and provide a path to ground for the energy in the positive powerline conductor 42 a. As previously explained, this effectively disconnects the positive powerline conductor 42 a from the rectifier 44. Plot 400D shows the negative switch control signal V_(g−) changing state (e.g., from low to high) at t₂, which in turn causes the negative powerline switch 50 b to change state (i.e., close).

Similarly, for the negative powerline conductor 42 b, the switch controller 54 may wait half a clock cycle until t₃ when the negative powerline voltage V_(p−) and the corresponding negative sensor voltage, V_(zero−) reaches a zero-voltage crossing point, controlled by a delay circuit (not shown), to close (turn on) the positive powerline switch 50 a and provide a path to ground for the energy in the negative powerline conductor 42 b, effectively disconnecting the negative powerline conductor 42 b from the rectifier 44. Because the positive powerline conductor voltage V_(p+) has already been shut to ground, the negative powerline conductor voltage V_(p−) may be abnormal and can no longer be used as a clock. Thus, the delay circuit may be employed to close the positive powerline switch 50 a when the negative powerline voltage V_(p−) and the corresponding negative sensor voltage V_(zero−) reaches a zero-voltage crossing point. Since the frequency of the negative powerline voltage V_(p−) is known, the delay circuit may be designed to delay t₃ until the negative powerline voltage V_(p−) is zero.

Plot 400H shows the positive switch control signal V_(g)+ changing state (e.g., from low to high) at t₃, which in turn causes the positive powerline switch 50 a to change state (i.e., close). As a result, the AC power from the receive antenna 18 may be dumped before it reaches the rectifier 44, effectively shutting down the wireless charger output 40 and protecting the vehicle battery 38. According to an embodiment, the switch control signals V_(g−) and V_(g+), whichever occurs first, may be clock edge triggered, and can only change state at the edge of the clock signal V_(clock). As shown, t₂ is at the edge of the clock signal V_(clock), while t₃ is delayed by a calculated delay time.

FIG. 5 illustrates an alternative timing diagram in which the switch controller 54 employs a grace period when outputting the negative switch control signal V_(g−). Plot 400C in FIG. 5 is the same as Plot 400C shown in FIG. 4. Plot 400D′ is a modified version of plot 400D shown in FIG. 4. Plot 400D′ shows a grace period θ on either side of t₂. As an example, the grace period θ may be +/−5 degrees from t₂ when the positive powerline conductor voltage V_(p+) and the positive sensor voltage V_(zero+) cross at zero volts. In this embodiment, the switch controller may output the negative switch control signal V_(g−) at t_(2′). Therefore, as long as t₂′, at which the negative switch control signal V_(g)− changes state, is within +/− the grace period θ, the circuit operation may be deemed as zero voltage switching. Though not shown, the same grace period θ may also apply to the positive switch control signal V_(g+) changing state.

FIG. 6 is a flowchart illustrating a process 600 for switching off a wireless charger output. At operation 602, the monitoring circuit 56 monitors the charging of the vehicle battery 38. At operation 604, the monitoring circuit 56 may determine whether a charging error is detected. If no such error is detected, the process returns to operation 602 and the monitoring circuit 42 continues to monitor the charging of vehicle battery 38. If a charging error is detected, the process proceeds to operation 606. As an example, the charging error may include over voltage, over current, microprocessor watchdog error, over temperature, in-vehicle network communication error, base unit error, and/or wireless communication error.

At operation 606, the switch controller 54 may receive an error signal V_(e) indicative of the charging error from the monitoring circuit 56. In response, at operation 608, the switch controller 54 may determine whether a powerline sensor voltage V_(zero+) or V_(zero−) received from the respective powerline sensors 48 indicates a zero-voltage crossing point of one of the powerline conductor voltages, V_(p+) or V_(p−). If not, the process may return to operation 608 and the switch controller 54 may wait until a first sensor voltage crosses zero volts. If so, the process may proceed to operation 610.

At operation 610, the switch controller 54 may output a switch control signal causing a switch connected to the powerline to change state (e.g., close) when a powerline sensor voltage, V_(zero+) or V_(zero−), indicates zero-voltage crossing. For example, if the output, V_(zero+), of the positive powerline sensor 48 a, sensing the positive powerline conductor voltage V_(p+), indicates the positive powerline conductor voltage V_(p+) crossing zero volts first (i.e., before the negative powerline conductor voltage V_(p−)), the switch controller 54 may cause the negative switch control signal V_(g−) to the negative powerline switch 50 b to change state. Consequently, the negative powerline switch 50 b may change state (i.e., close) during the zero-voltage crossing point of the positive powerline conductor voltage V_(p+) to protect the switch and provide a path to ground for dumping energy in the receive antenna 18. Then, the process may return to operations 608 and 610 to similarly close the positive powerline switch 50 a when the negative powerline conductor voltage V_(p−) reaches a zero-voltage crossing point.

Alternately, if the output, V_(zero+), of the negative powerline sensor 48 b, sensing the negative powerline conductor voltage V_(p−), indicates the negative powerline conductor voltage V_(p−) crossing zero volts first (i.e., before the positive powerline conductor voltage V_(p+)), the switch controller 54 may cause the positive switch control signal V_(g+) to the positive powerline switch 50 a to change state. Consequently, the positive powerline switch 50 a may change state (i.e., close) during the zero-voltage crossing point to protect the switch and provide a path to ground for dumping energy in the receive antenna 18. Then, the process may return to operations 608 and 610 to similarly close the negative powerline switch 50 b when the positive powerline conductor voltage V_(p+) reaches a zero-voltage crossing point. After repeating operations 608 and 610, the process may end at operation 612.

While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the present invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the present invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the present invention. 

What is claimed is:
 1. A wireless charger output protection system comprising: a monitoring circuit connected to an output of a wireless charging unit, the monitoring circuit configured to output an error signal in response to detecting a charging error; a powerline sensor configured to output a voltage signal indicative of a powerline voltage of a powerline; and a switch controller, in communication with the monitoring circuit and the powerline sensor, configured to: receive the error signal and the voltage signal; and output a switch control signal, in response to the error signal, to a switch causing the switch to change state and disconnect the powerline from a battery when the voltage signal indicates a zero-voltage crossing point.
 2. The system of claim 1, wherein the switch controller outputs the switch control signal within a grace period from the time when the voltage signal indicates a zero-voltage crossing point.
 3. The system of claim 1, wherein the powerline is configured to transmit AC current induced in a receive antenna.
 4. The system of claim 3, further comprising a rectifier configured to rectify the AC current from the powerline into a DC current for charging a battery.
 5. The system of claim 4, wherein the switch, connected to the powerline, is configured to control electrical connection between the receive antenna and the rectifier.
 6. The system of claim 1, wherein the switch comprises an insulated-gate bipolar transistor (IGBT) having a gate that is connected to the switch controller.
 7. The system of claim 6, wherein the IGBT lacks a body diode.
 8. A method for switching off a wireless charger output, the wireless charger including a powerline having a positive powerline conductor and a negative powerline conductor for transmitting AC power, and a rectifier for converting the AC power from the powerline into DC power, the method comprising: receiving, at a switch controller, an error signal indicative of a charging error from a battery monitoring circuit; receiving, at the switch controller, a positive voltage signal indicative of a positive powerline voltage from a positive powerline sensor in sensing relation to the positive powerline conductor; receiving, at the switch controller, a negative voltage signal indicative of a negative powerline voltage from a negative powerline sensor in sensing relation to the negative powerline conductor; and outputting, by the switch controller, in response to the error signal, a negative switch control signal to a negative switch connected to the positive powerline conductor causing the negative switch to change state when the positive voltage signal received from the positive powerline sensor indicates a zero-voltage crossing point.
 9. The method of claim 8, wherein causing the negative switch to change state connects the positive powerline conductor to ground.
 10. The method of claim 8, wherein the negative switch changes state within a grace period from the time when the positive voltage signal indicates a zero-voltage crossing point.
 11. The method of claim 8, further comprising: outputting, by the switch controller, subsequent to the negative switch control signal, a positive switch control signal to a positive switch connected to the negative powerline conductor causing the positive switch to change state when the negative voltage signal received from the negative powerline sensor indicates a zero-voltage crossing point.
 12. The method of claim 11, wherein causing the positive switch to change state connects the negative powerline conductor to ground.
 13. The method of claim 11, wherein the positive switch changes state within a grace period from the time when the negative voltage signal indicates a zero-voltage crossing point.
 14. The method of claim 8, further comprising: monitoring charging of a vehicle battery by the battery monitoring circuit; and sending the error signal from the battery monitoring circuit to the switch controller upon detection of the charging error.
 15. The method of claim 14, wherein the charging error includes at least one of over voltage, over current, and over temperature of the vehicle battery.
 16. The method of claim 14, wherein the charging error includes a communication error.
 17. A wireless charging unit comprising: a powerline sensor, in sensing relation to a powerline, configured to output a voltage signal indicative of a powerline voltage; a switch, connected to the powerline, configured to control electrical connection between a receive antenna and a rectifier; and a switch controller, connected to the powerline sensor and the switch, configured to receive an error signal indicative of a charging error from a monitoring circuit and output a switch control signal causing the switch to change state, in response to the error signal, when the voltage signal received from the powerline sensor indicates a zero-voltage crossing point.
 18. The wireless charging unit of claim 17, wherein the powerline is configured to transmit AC current induced in the receive antenna and the rectifier is configured to rectify the AC current from the powerline into a DC current for charging a vehicle battery.
 19. The wireless charging unit of claim 17, wherein the switch controller outputs the switch control signal within a grace period from the time when the voltage signal indicates a zero-voltage crossing point.
 20. The wireless charging unit of claim 17, wherein the voltage signal is substantially in phase with an AC powerline voltage that is input into the powerline sensor with a smaller voltage amplitude. 